Begell House Inc.International Journal of Energetic Materials and Chemical PropulsionIJEMCP2150-766X1462015FORMULATION, CASTING, AND EVALUATION OF PARAFFIN-BASED SOLID FUELS CONTAINING ENERGETIC AND NOVEL ADDITIVES FOR HYBRID ROCKETS453-478Daniel B.LarsonThe Pennsylvania State University, University Park, Pennsylvania 16802, USAJohn D.DeSainThe Aerospace Corporation, El Segundo, California 90245, USAEricBoyerThe Pennsylvania State University, University Park, Pennsylvania 16802, USATrevor WachsThe Pennsylvania State University, University Park, Pennsylvania 16802, USAKenneth K.KuoDepartment of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802, USARussell BorduinUniversity of Texas−Austin, Austin, Texas 78712, USA Joseph H.KooUniversity of Texas−Austin, Austin, Texas 78712, USA Brian B. BradyThe Aerospace Corporation, El Segundo, California 90245, USAThomas J. CurtissThe Aerospace Corporation, El Segundo, California 90245, USAGeorge StoryNASA-Marshall Space Flight Center, Huntsville, Alabama 35811, USAThis investigation studied the inclusion of various additives to paraffin wax for use in a hybrid rocket motor. Some of the paraffin-based fuels were doped with various percentages of LiAlH4 (up to 10%). Addition of LiAlH4 at 10% was found to increase regression rates between 7 and 10% over baseline paraffin through tests in a gaseous oxygen hybrid rocket motor. Mass burn rates for paraffin grains with 10% LiAlH4 were also higher than those of the baseline paraffin. RDX (or cyclotrimethylenetrinitramine, C3H6N6O6) was also cast into a paraffin sample via a novel casting process which involved dissolving RDX into dimethylformamide (DMF) solvent and then drawing a vacuum on the mixture of paraffin and RDX/DMF in order to evaporate out the DMF. It was found that although all the DMF was removed, the process was not conducive to generating small RDX particles. The slow boiling generated an inhomogeneous mixture of paraffin and RDX. It is likely that superheating the DMF to cause rapid boiling would likely reduce RDX particle sizes. In addition to paraffin/LiAlH4 grains, multiwalled carbon nanotubes (MWNT) were cast in paraffin for testing in a hybrid rocket motor, and assorted samples containing a range of MWNT percentages in paraffin were imaged using scanning electron microscopy and thermally tested using thermogravimetric analysis. The fuel samples showed good distribution of MWNT in the paraffin matrix, but the MWNT were often agglomerated, indicating that a change to the sonication and mixing processes is required to achieve better uniformity and debundled MWNT. Fuel grains with MWNT fuel grains had a slightly lower regression rate, likely due to the increased thermal conductivity to the fuel subsurface, reducing the burning surface temperature.SIMULATION OF IGNITION AND COMBUSTION OF LOW-VULNERABILITY PROPELLANT FOR ARTILLERY479-498ChristopheBoulnoisNEXTER Munitions, 7 Route de Guerry, 18000 Bourges, France; PRISME EA 4229, Univ. Orleans, 63 Avenue de Lattre de Tassigny, 18000 Bourges, FrancePhilippeGillardUniversity of Orléans, INSA-CVL, PRISME EA 4229, Bourges, FranceCamilleStrozziInstitut PPRIME, UPR 3346 du CNRS, Univ. Poitiers, 1 Avenue Clement Ader, Futuroscope, Chasseneuil, France
Amar BouchamaDGA Techniques Terrestres, Echangeur de Guerry, 18000 Bourges, FranceThis paper deals with a novel approach to numerically simulate the ignition and combustion of a bed of grains consisting of low-vulnerability ammunitions (LoVA) propellants in a gun tube. The originality of the work relies on a dual approach, since the same combustion wave model is used both for ignition and stationary combustion near the surface of the propellant grains. The rate of decomposition for propellant grains is written in terms of a transient one-dimensional heat equation inside the solid with a heat source. This heat source is related to the flame structure developing at the burning propellant surface and allows sustaining the thermal decomposition process in a stationary combustion. This stationary combustion follows the Vieille's law and the attainment of ignition depends on the level of incoming heat flux. Another aspect of the modelling is related to the porous medium, which is taken into account since spherical grains are packed inside the gun combustion chamber. Fluid flow equations for the gas phase are written with a full compressible flow in 2D transient formulation and a multistep reaction source is considered in the energy equation. Finally, the propagation of the combustion front after ignition during the early stages of the internal ballistic cycle of the gun tube is considered in a simplified geometry. The results are compared to the experimental Vieille's law of the propellant, showing the relevance of the proposed approach for future multidimensional studies.THE SENSITIVITY OF CHEMICAL KINETICS WITH TWO CHARACTERISTIC LENGTHS OF DETONATION DYNAMICS IN HOMOGENEOUS GASES499-517StephaneBoulalInstitute Pprime (UPR 3346 CNRS) Fluid, Thermal and Combustion Sciences Department ENSMA, BP 40109, 86960 Futuroscope-Chasseneuil, France; SAFRAN-SNECMA, Etablissement de Villaroche, 77550 Moissy Cramayel, FrancePierre VidalInstitute Pprime (UPR 3346 CNRS) Fluid, Thermal and Combustion Sciences Department ENSMA, BP 40109, 86960 Futuroscope-Chasseneuil, FranceRatiba ZitounInstitute Pprime (UPR 3346 CNRS) Fluid, Thermal and Combustion Sciences Department ENSMA, BP 40109, 86960 Futuroscope-Chasseneuil, FranceJocelyn LucheInstitute Pprime (UPR 3346 CNRS) Fluid, Thermal and Combustion Sciences Department ENSMA, BP 40109, 86960 Futuroscope-Chasseneuil, FranceThis work discusses the sensitivity of chemical kinetics with two characteristic lengths of detonation dynamics calculated with a steady, weakly diverging, reaction-zone model. These are the chemical lengths defined as the distance from the detonation leading shock to the inflection point of the temperature profile and the minimum radius for the existence of a self-sustained, spherically diverging detonation. Two detailed chemical kinetic mechanisms are implemented in the model to estimate the characteristic lengths for H2/O2 and H2/air mixtures at different equivalence ratios and initial pressures. A high sensitivity to the chemical kinetic scheme is obtained, with discrepancies ranging from 20% to 80%. Calculated and measured critical radii are found to be of the same order, which supports the premise of this work to assess sensitivity from a hydrodynamic model rather than from unsteady 3D simulations. Nevertheless, the differences are very important, especially at higher initial pressures. Importantly, these large differences from one scheme to the other are of the same order as between experimental data themselves. The same high sensitivity should thus be expected from numerical simulations and, therefore, chemical kinetics requires proper calibration in a large range of initial pressures to reproduce experimentally observed detonation dynamics. The predictive ability of simulations should be considered with caution, especially if detailed chemical kinetic schemes are implemented. Detonation studies should remain driven by experiments and sound dimensional analysis. More fundamental work aimed at improving high-pressure, high-temperature chemical kinetics is necessary before simulation can be used as an effective design tool for detonation-based propulsive devices such as pulsed or rotating detonation engines.VIBRATIONAL AND THERMODYNAMIC PROPERTIES OF 1,3,5-TRIAMINO-2,4,6-TRINITROBENZENE (TATB): COMPARISON OF EXCHANGE-CORRELATION FUNCTIONALS IN DENSITY FUNCTIONAL THEORY519-547Zhongqing WuCollaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, and Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242, USA; School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, ChinaWeiwei MouCollaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, and Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242, USARajiv K. KaliaCollaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, and Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242, USAAiichiro NakanoCollaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, and Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242, USAPriyaVashishtaCollaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, and Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242, USAVibrational and thermodynamic properties of TATB have been investigated within the quasiharmonic approximation and density functional theory using three exchange-correlation functionals: local density approximation (LDA), generalized gradient approximation (GGA), and GGA with an empirical van der Waals correction (GGA + vdW). We find that GGA provides a reasonable description of only the heat capacity and thermal expansion, while it fails to reproduce the experimental bulk modulus and volume. Van der Waals correction improves the lattice constants, volume, and bulk modulus, but it fails badly in describing thermal expansion and heat capacity. In contrast, LDA accurately describes all the thermodynamic properties of TATB considered here. For example, the equilibrium volume calculated with LDA is only 4.6% smaller than the experimental value after including vibrational contributions. It is therefore essential to include phonon contributions when comparing the calculated volume with experimental data at ambient conditions. We show that an accurate equation of state of TATB is obtained by simply multiplying the volume calculated with LDA by a factor of 1.046, because LDA predicts the bulk modulus well in the entire pressure range. Therefore, LDA is a satisfactory exchange-correlation functional for TATB because only LDA correctly predicts the volume dependence of vibrational frequencies. All calculations exhibit an abrupt change of the compressibility at a critical pressure, Pc ~ 0.5−1.0 GPa. Below Pc, the volume reduction by pressure is mainly due to the lattice contraction along the c axis, whereas above Pc the lattice contracts significantly along all three axes.Contents Volume 14, 2015549-554